The Caribbean Sea is battling an epidemic — a nasty plague that spreads and kills quickly. Unlike the historical Black Plague, which killed millions of people in the Middle Ages, this so-called white plague is devastating populations of marine corals.

Scientists long believed the scourge, which first popped up in the 1970s, had strictly bacterial origins, but research now suggests viruses may play a prominent role in causing white plague.

During a 2010 white plague outbreak in the Virgin Islands, researchers analyzed the viruses present in diseased and healthy corals. While all of the sampled corals carried numerous viruses, the tissue taken from corals that had white plague predominately contained one, specific group of viruses. Known as small, circular, single-strand DNA viruses (SCSDV), these could potentially have caused the disease.